Intravenous administration of tramadol

ABSTRACT

A method of treating pain, e.g., acute post-operative pain, by intravenously administering to a human patient(s) a dose of tramadol of about 45 mg to about 80 mg, based on tramadol hydrochloride, together with an intravenous dose of acetaminophen in an amount from about 500 mg to about 1000 mg, about every 6 hours.

BACKGROUND OF THE INVENTION

Tramadol is a centrally acting synthetic analgesic with a dual mechanism of action attributed to the racemic form of the drug, comprised of μ-opioid activity (binding to μ-opioid receptors and monoamine (serotonin and noradrenalin) reuptake inhibition. Tramadol is an analog of the phenanthrene group of opium alkaloids, which includes morphine and codeine, and is structurally related to these opioids (Grond S and Slabotzi A. Clinical pharmacology of tramadol. Clin Pharmacokinet. 2004; 43:879-923). Like codeine, there is a substitution of the methyl group on the phenol ring that imparts a relatively weak affinity for opioid receptors. (+)-Tramadol is a more potent inhibitor of serotonin uptake, while (−)-tramadol is a more potent inhibitor of norepinephrine uptake. The opioid-like activity of tramadol derives from low affinity binding of the parent compound to μ-opioid receptors and higher affinity binding of its main metabolite. Tramadol affinity to μ opioid receptors is about 10 times weaker than codeine 60 times weaker than dextropropoxyphene and 6,000 times weaker than morphine. The active metabolite O-desmethyltramadol (M1) possesses a higher affinity to the μ opioid receptor than tramadol and displays analgesic activity (Leppert W, 2009).

Tramadol was originally developed by the German pharmaceutical company Grunenthal GmbH in the late 1970s and is marketed globally under the trade names TRAMAL® and others outside of the United States. The approved doses of tramadol are 50 mg or 100 mg administered as a slow injection every 4-6 hours (Tramadol Core Product Label, 2008). In the U.S., tramadol is approved by the Food and Drug Administration (FDA) and marketed as an oral capsule/tablet for moderate to moderately severe pain in adults. Tramadol was first approved in the US in April 1995 under the trade name, ULTRAM® (Ortho-McNeil-Janssen Pharmaceuticals, Inc). Tramadol is also an active agent in an extended release product, Ultram® ER, and a combination product with acetaminophen, ULTRACET®. In the US, tramadol is only available as immediate release tablets or extended release tablets. Other tramadol formulations approved in several countries include tablets, capsules, effervescent powders, and suppositories (Grond and Sablotzki, 2004; Rosenberg, 2009). The approved intravenous regimen in India is an initial injection of 50 mg infusion over 2-3 min, followed by 50 mg every 10-20 minutes if necessary up to 250 mg for the first hour. Maintenance doses are 50-100 mg every 4-6 hours with a maximum dose of 600 mg daily (Tramadol, CIMS Data_India).

Postoperative pain management with tramadol has effectively utilized a variety of delivery methods, including bolus injection (IV or IM), continuous infusions and patient controlled analgesia (PCA) pumps, and various combinations of these methods (Scott and Perry, 2000; Grond and Sablotzki, 2004). The potency ratio of IV tramadol to IV morphine is approximately 1:10, while the ratio for IV fentanyl is 1:979 (Grond and Sablotzki, 2004).

The “on-demand” analgesic efficacy of tramadol was compared to morphine in the 24-hour post-operative period for 523 patients undergoing abdominal surgery (Vickers M D, Paravicini D. Comparison of tramadol with morphine for post-operative pain following abdominal surgery. Eur J Anesthesiol. 1995; 12: 265-71). Patients who reported post-operative pain received an initial dose (either tramadol 100 mg or morphine 5 mg i.v.) and, if necessary, repeat i.v. or i.m. doses of tramadol 50 mg or morphine 5 mg on demand over the first 90 minutes. Further doses up to a total of 400 mg tramadol or 40 mg morphine could then be given after 90 minutes up to 24 hours after the first dose of study medication. The primary efficacy parameter was the responder rate (no or slight pain) within the first 90 minutes of treatment. Responder rates were 72.6% for tramadol and 81.2% for morphine, which were statistically equivalent and within the predefined range of ±10%. Mean cumulative doses were 188.2 mg for the first 90 minutes and 157.1 mg for the subsequent 22.5 hours in the tramadol group and 13.9 mg and 18.4 mg, respectively in the morphine group. The main adverse events were gastrointestinal in both groups, with mild nausea, dry mouth, vomiting, dyspepsia and hiccups reported most frequently.

The analgesic effect of continuous infusion of tramadol was compared to repeated bolus administration in 135 patients undergoing abdominal surgery (Rud U, Fischer M V, Mewes R, Paravcini D., “Postoperative Analgesie mit Tramadol Kontinuierliche Infusion versus repetitive” (Postoperative analgesia with tramadol. Continuous infusion versus repetitive bolus administration), Bolusgabe Anaesthesist. 1994; 43:316-321. (German)). Patients were randomized at the time of the first request for pain treatment. All patients received a loading dose of tramadol 100 mg i.v. Subsequent treatment was administered in a double-blind manner; patients in the infusion group were given a continuous infusion of tramadol 12 mg/h for 24 hours, whereas patients in the bolus group received placebo infusion. In both groups, additional bolus doses of tramadol 50 mg i.v. were given as required. Pain relief was monitored by means of a visual analog scale (VAS) up to 6 hours after surgery. The number of additional boluses and the amount of tramadol administered at 6 hours and 24 hours was also used to assess analgesic efficacy. More patients in the infusion group assessed their pain relief as excellent or good compared to the bolus group (76.5% vs 65.6%). Only a few patients complained of insufficient analgesia, with more patients in the bolus group reporting inadequate pain relief than in the infusion group (7.5% vs 4.4%). A higher percentage of patients in the bolus group required two or more boluses compared to the infusion group (59.7% vs 30.8%). After 6 hours, the average tramadol consumption was 223.5±53.7 mg in the infusion group and 176.6±63.1 mg in the bolus group (p≤0.05). After 24 hours, tramadol consumption was 449.5±66.0 mg and 201.6±83.9 mg (p≤0.001), respectively. Adverse events were reported by 25% of patients in both groups, with no significant differences and no patient terminated the trial for an adverse event. There were no significant effects on blood pressure or heart rate. The authors concluded that continuous infusion was more effective in the first 6 hours after surgery. However, excess consumption by the infusion group was statistically greater than the bolus group at both 6 hours and 24 hours post-surgery.

Intermittent bolus and continuous infusion of tramadol were evaluated in a postoperative study of 35 patients undergoing major abdominal gynecologic surgery (Chrubasik J, Buzina M, Schulte-Monting J, Atanassoff P, Alon E. Intravenous tramadol for post-operative pain-comparison of intermittent dose regimens with and without maintenance infusion. Eur J Anaesthesiol. 1992; 9:23-28). The study was randomized and double-blind and used tramadol infusion 15 mg/h or saline. Additional boluses of tramadol 100 mg were given as requested. The patients in the infusion group required 60% less tramadol on demand (p<0.01) and had better pain relief (p<0.05), as assessed by VAS, than the group that received the saline infusion. Total tramadol consumption, however, was about 30% higher in the infusion group (p<0.05) and was associated with and increased incidence of minor adverse events. Tramadol was ineffective as pain relief within 2 hours of the beginning of treatment in 6% of the infusion group and 20% of the bolus group. Thus, continuous infusion was preferred to “on-demand” bolus treatment.

A meta-analysis of nine randomized, controlled trials indicated that tramadol was as effective as other opioids, including morphine, for control of postoperative pain (Scott and Perry, 2000). Pain in these patients was described as moderate to severe, with initial postoperative pain reported as >60 on a 100-point visual analog scale or as moderate or severe on a 4- or 5-point verbal response scale. The first dose of analgesia was administered when patients reported moderate to severe pain in the postoperative setting. Studies that did not adequately record baseline pain severity or response to analgesia, were not randomized or controlled or contained less than 45 patients were excluded from the meta-analysis. Tramadol, administered in a dose titrated to pain response and via either IV (intravenous) or IM (intramuscular) intermittent injection, reduced pain intensity by 46.8% to 57.6% after 4 to 6 hours compared to 69.8% for morphine and 25.6% to 51.3% for pentazocine. Efficacy of tramadol was maintained for the duration of the studies, which were ≤72 hours, and was comparable to morphine or alfentanil. However, the onset of action of tramadol was slower than morphine, as assessed by measurements approximately 3 hours after the first dose. There were no significant differences in the percentage of patients treated with tramadol or morphine and who also required rescue medication. The patient global response and physician global response were similar for tramadol and for other opioids.

Tramadol injection (IV/IM/SC) is approved and used for the management of moderate to severe acute postoperative pain in several regions, including Europe, India and Australia/New Zealand (however, this dosage form is not available in the USA). Tramadol ampoules or vials for IV, IM and SC administration and preservative-free solutions for injection by the various spinal routes (epidural, intrathecal, caudal, etc.) are available forms in these regions. Tramadol formulations approved in several countries include, tablets, capsules, effervescent powders, and suppositories (Grond and Sablotzki, 2004; Rosenberg, 2009).

There is extensive data demonstrating that tramadol use is not associated with the classical opioid side effects seen with more potent opioids. There are numerous reports of the safety and efficacy of tramadol (Lee et al., 1993; Scott and Perry, 2000; Grond and Sablotzki, 2004). The most common adverse events of tramadol administration are nausea, dizziness, headache, somnolence, sweating, fatigue, constipation, dry mouth and vomiting. However, tramadol use, particularly with high doses, has been associated with seizures, and the risk of seizures is increased in the presence of drugs that reduce seizure threshold, head trauma or prior history of seizures.

Patients undergoing surgery, for example, total knee arthroplasty (TKA) and total hip arthroplasty (THA), typically demonstrate a need for short-term analgesia, which is critical for earlier mobilization and rehabilitation. In this setting, assuring adequate pain relief without providing extensive medical oversight required for some methods of treatment (such as neuraxial anesthesia) and prevention of effects such as opiate-induced respiratory depression and dependency would be highly beneficial (Sinatra et al., 2002).

The goal of post-surgical pain management is twofold: i) to provide a quick onset of analgesic or pain relief and ii) to reduce or modulate the quality and intensity of pain that a patient experiences in the post-surgical period. While current treatments for management of post-surgical acute pain are useful, there is a need for improved methods for treating post-surgical acute pain.

Prior publications report that analgesic potency may be improved while reducing undesirable effects by combining an opioid with an NSAID or an analgesic such as acetylsalicylic acid or acetaminophen, in such a way as to obtain a synergistic analgesic effect allowing for a reduction in the total dose of both the NSAID and analgesic. For example, U.S. Pat. No. 4,569,937, issued to Baker et al. on Feb. 11, 1986, describes a combination of oxycodone with ibuprofen in a ratio of oxycodone/ibuprofen from 1:6 to about 1:400. U.S. Pat. No. 4,690,927, issued to Voss et al. on Sep. 1, 1987, describes a combination of the NSAID diclofenac and codeine in a weight ratio of diclofenac to codeine of about 1:1 to about 3:1. U.S. Pat. No. 5,190,947, issued to Riess et al. on Mar. 2, 1993, describes a diclofenac-codeine salt ([2-[2,6-dichlorophenyl)-amino]-phenyl]-acetic acid). U.S. Pat. No. 4,844,907, issued to Elger et al. on Jul. 4, 1989, describes a multiphase tablet combining a narcotic analgesic phase and an NSAID phase in separate layers. U.S. Pat. No. 4,587,252, issued to Arnold et al. on May 6, 1986, describes a process for treating pain using a combination of hydrocodone and ibuprofen.

OBJECTS AND SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method of treating pain in human patients.

It is a further object of the present invention to provide a method of treating pain in human patients who are unable to take oral medications, such as in a post-operative condition.

It is a further object of the present invention to provide a method of treating pain in human patients that takes advantage of the faster onset of intravenous administration of tramadol while providing additional benefits not available via current methodologies of tramadol intravenous administration.

It is another object of the present invention to provide a method of providing a safe and effective alternative injectable analgesic for use in the acute postoperative setting.

It is another object of the present invention to provide a method for treating pain in, e.g., the acute postoperative setting which is or may be opioid-sparing.

It is another object of the present invention to provide a method for treating pain with intravenous tramadol in human patients in a manner that may or does reduce side-effects (such as, e.g., nausea, vomiting or seizure).

It is a further object of the present invention to provide a method of treating pain with a drug and dosing regimen that provides a positive benefit-risk profile, and which addresses an unmet medical need for the management of acute postoperative pain.

In accordance with the above objects and others, the present invention is directed in part to the co-administration of intravenous tramadol and intravenous acetaminophen to a human patient(s) to treat acute pain. In certain embodiments, the co-administration occurs either prior to, during, or after surgery.

In accordance with the above objects and others, the present invention is directed in part to a method of administering tramadol for treating pain via an intravenous dosing regimen comprising intravenously administering a first dose of tramadol to a human patient in an amount from about 45 mg to about 80 mg; and concurrently administering an intravenous dose of acetaminophen in an amount from about 500 mg to about 1,000 mg; and thereafter intravenously administering the doses of tramadol and acetaminophen about every 5 to about every 7 hours, preferably about every 6 hours until the patient no longer requires treatment with intravenous tramadol. The intravenous dosing regimen provides a Cmax of tramadol which is similar to the Cmax of an oral dose of 100 mg tramadol HCl given every 6 hours at steady-state. In certain preferred embodiments, each dose of tramadol is about 60 mg. The intravenous dosing regimen preferably provides a Cmax of tramadol which is similar to the Cmax of an oral dose of 100 mg tramadol HCl given every 6 hours at steady-state. In certain preferred embodiments, each dose of tramadol is about 60 mg tramadol hydrochloride. In certain further preferred embodiments, each dose of acetaminophen is about 650 to about 750 mg.

In certain preferred embodiments, the intravenous dosing regimen of the invention provide a Cmax of tramadol at steady-state that is from about 80% to about 125% of the Cmax provided at steady-state by a 100 mg oral dose of tramadol HCl given every 6 hours, e.g., the intravenous dosing regimen provides a Cmax of tramadol at steady-state from about 80% to about 125% of about 736 ng/mL. The method may further comprise continuing to administer additional doses of tramadol and acetaminophen to the human patient for at least about 42 hours after the first administered dose of tramadol.

In certain preferred embodiments, the method further comprises diluting the dose of tramadol and acetaminophen in from about 50 ml to about 500 ml of a pharmaceutically acceptable fluid for injection, and standardizing the administration of the injection of the dose of tramadol and acetaminophen via the use of a pump. The dose may be provided in the form of a sterile solution at a concentration of about 60 mg tramadol hydrochloride and from about 500 mg to about 1,000, preferably from about acetaminophen contained in one or more ampoules or vials. The ampoules may contain the dose of tramadol together acetaminophen with a buffering agent in solution for injection, or the ampoules/vials may separately contain the dose of tramadol in one ampoule and the dose of acetaminophen in another ampoule. In certain embodiments, the method further comprises diluting the dose of tramadol and acetaminophen into an IV bag for administration to the human patient.

The first dose of tramadol/acetaminophen may be administered to the human patient intra-operatively at wound closure, or from first demand of analgesia postoperatively, and administering further doses of intravenous tramadol/acetaminophen for at least two days post-surgery. In certain embodiments, the human patient is suffering from acute post-operative pain.

The method may further comprise switching the human patient after at least three intravenous doses of tramadol/acetaminophen, to oral doses of the same amount of tramadol and acetaminophen previously administered intravenously, such that the Cmax of tramadol at the time the human patient is switched to oral doses is similar to the Cmax provided at steady-state by a dosing regimen of 100 mg tramadol HCl administered orally every 6 hours.

The method may further comprise administering an opioid analgesic which is not tramadol to the human patient to treat breakthrough pain.

In certain preferred embodiments, the invention is directed to a method of administering tramadol for treating pain via an intravenous dosing regimen, comprising intravenously administering a first dose of tramadol to a human patient in an amount of about 45 mg to about 80 mg (e.g., about 60 mg); and concurrently administering an intravenous dose of acetaminophen in an amount of about 500 to 1,000 mg (e.g., about 650 mg); and thereafter intravenously administering the doses of tramadol and acetaminophen about every 5 to about 7 hours (e.g., preferably about every 6 hours) until the patient no longer requires treatment with intravenous tramadol, wherein the tramadol is tramadol base or a pharmaceutically acceptable salt of tramadol, such that the intravenous dosing regimen provides a Cmax of tramadol which is similar to the Cmax of an oral dose of 100 mg tramadol HCl given every 6 hours at steady-state. The intravenous dosing regimen of the invention preferably provides a Cmax of tramadol at steady-state that is from about 80% to about 125% of the Cmax provided at steady-state by a 100 mg oral dose of tramadol HCl given every 6 hours, e.g., the intravenous dosing regimen provides a Cmax of tramadol at steady-state from about 80% to about 125% of about 736 ng/mL.

In certain preferred embodiments, the intravenous dosing regimens of the invention provide a Cmax of the M1 metabolite of tramadol at steady-state that is from about 20% to about 125% (in certain embodiments from about 60% to about 75%), or from about 80% to about 125% of the Cmax of the M1 metabolite of tramadol at steady-state when the tramadol is administered as oral 100 mg tramadol HCl every 6 hours.

In certain embodiments of the intravenous dosing regimens of the invention, the intravenous dosing regimen provides a Cmax of tramadol at steady-state from about 80% to about 125% of about 736 ng/mL.

In preferred embodiments of the intravenous dosing regimens of the invention, each dose of tramadol and acetaminophen is administered intravenously over a time period from about 10 minutes to about 20 minutes. In certain preferred embodiments, each dose of the tramadol and acetaminophen is administered over a time interval of 15 (±2) minutes.

In certain preferred embodiments of the intravenous dosing regimens of the invention, the method further comprises administering a first intravenous dose of tramadol and acetaminophen to the patient intra-operatively at wound closure, or from first demand of analgesia post-operatively, and administering said further doses of intravenous tramadol for at least two days post-surgery.

In certain preferred embodiments of the intravenous dosing regimens of the invention, the method further comprises administering one or more doses of an intravenous opioid analgesic as rescue medicine to the patient to treat breakthrough pain.

In certain preferred embodiments of the intravenous dosing regimens of the invention, the method further comprises administering the first dose of tramadol and acetaminophen on first demand of analgesia post-operatively, further comprising administering a therapeutically effective dose intravenous opioid analgesic to the patient at the end of the surgery.

In certain preferred embodiments of the intravenous dosing regimens of the invention, the method further comprises administering the first dose of tramadol and acetaminophen to the patient intra-operatively at wound closure, further comprising administering a bolus of a therapeutically effective dose of intravenous opioid analgesic to the patient if the patient requests analgesia before the second dose of intravenous tramadol/acetaminophen.

In certain preferred embodiments of the intravenous dosing regimens of the invention, the method further comprises administering a rescue opioid analgesic using Patient Controlled Analgesia (PCA).

In certain preferred embodiments of the intravenous dosing regimens of the invention, the treatment of pain in the patient is conventional opioid-sparing over the first, e.g., 24, 30, 36, 42 or 48 hours post-surgery.

In certain preferred embodiments of the intravenous dosing regimens of the invention, the method further comprises diluting tramadol in a volume of normal saline to provide a unit dose from about 45 mg to about 80 mg tramadol and from about 500 to about 1,000 mg acetaminophen in a volume of normal saline; administering the dose intravenously over a time period, e.g., from about 15 (±2) minutes. In certain preferred embodiments of the intravenous dosing regimens of the invention, the method further comprises diluting tramadol in a volume of normal saline to provide a unit dose of about 60 mg tramadol and from about 650 to about 750 mg acetaminophen in a volume of normal saline; administering the dose intravenously over a time period, e.g., from about 15 (±2) minutes.

In certain preferred embodiments of the intravenous dosing regimens of the invention, the dose prior to dilution is contained in one or more ampoules.

In certain preferred embodiments of the intravenous dosing regimens of the invention, the ampoules contain tramadol hydrochloride, acetaminophen, and a buffering agent in water for injection.

In certain embodiments of the intravenous dosing regimens of the invention, the human patient(s) is suffering from acute post-operative pain.

In certain preferred embodiments of the intravenous dosing regimens of the invention, the method provides a reduction in at least one side-effect associated with tramadol therapy (e.g., as compared to prior art intravenous dosing regimens), wherein the side-effect is nausea, vomiting, or seizure.

In certain preferred embodiments of the intravenous dosing regimens of the invention, the method further comprises administering a therapeutically effective dose of an intravenous opioid analgesic is administered to the patient (i) at the end of the surgery, (ii) if the patient requests analgesia before the second dose of tramadol, or (iii) both (i) and (ii).

In certain preferred embodiments, the present invention is directed in part to a method of treating pain, comprising administering to a human patient(s) a therapeutically effective dose of tramadol and acetaminophen intravenously over a time period from about 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 21, 22, 23, 24, 25, 26, 27, 28, 29 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44 or 45 minutes.

Further aspects of the invention are directed to diluting the dose of tramadol and acetaminophen in from about 50 ml to about 500 ml (and preferably from about 50 ml to about 100 ml) of a pharmaceutically acceptable fluid for injection such as normal saline, e.g., in a bag or vial, and standardizing the administration of the injection of the dose of tramadol and acetaminophen via the use of a pump. In another embodiment, the dose is provided in the form of a sterile solution composed of about 60 mg tramadol hydrochloride and about 500 to 1,000 mg.

In certain further preferred embodiments, the dose of tramadol prior to dilution is contained in one or more ampoules. In certain preferred embodiments, the ampoules may contain the dose of tramadol (e.g., tramadol hydrochloride) together acetaminophen, alone or with a buffering agent (e.g., sodium acetate) in water for injection (e.g., about 1 ml to about 5 ml).

In certain further preferred embodiments, the method further comprises diluting the dose of tramadol and acetaminophen into an IV bag or ampoule/vial for administration to the patient.

In certain preferred embodiments of the present invention, the method further comprises administering a first dose of tramadol/acetaminophen to the patient intra-operatively at wound closure, or from first demand of analgesia postoperatively, and administering said further doses of intravenous tramadol/acetaminophen for at least two days post-surgery.

In certain preferred embodiments of the present invention, the method further comprises the concomitant administration of one or more opioid analgesics, preferably via the injectable (e.g., intravenous) route as rescue medicine to the patient to treat breakthrough pain that the patient experiences, e.g., for the time period of at least about 48 hours post-surgery. Several options are available for postoperative pain management (Singelyn et al., 1998; Sinatra et al., 2002; both of which are hereby incorporated by reference). Options include intermittent “on-demand” analgesia, continuous epidural analgesia with opioids and/or local anesthetics is effective, or to provide a combination of nerve blocks with long-acting local anesthetics and/or opioids initiated intra-operatively and continued into the immediate postoperative period. For example, most Total knee Arthroplasty (TKA) or Total Hip Arthroplasty (THA) procedures are currently performed with regional (or neuraxial) or other nerve blocks and without general anesthesia. In certain preferred embodiments of the invention, the method further comprises administering a rescue opioid analgesic using Patient Controlled Analgesia (PCA). In certain preferred embodiments, the intravenous administration of opioid analgesic also or alternatively comprises opioid analgesic (e.g., morphine) intravenously to the patient at an effective dose (e.g., morphine in an amount of about 0.05 mg/kg) as a bolus at the end of surgery or upon first demand of analgesia postoperatively, to provide effective analgesia to the patient(s).

In certain preferred embodiments of the invention, the first dose of tramadol is administered on first demand of analgesia postoperatively. Thereafter, the method may further comprise administering a therapeutically (analgesically) effective dose intravenous opioid analgesic to the patient at the end of the surgery, to provide effective analgesia to the patient(s).

In certain preferred embodiments of the invention, the first dose of tramadol is administered to the patient intra-operatively at wound closure. In such embodiments, the method may further comprise administering a bolus of a therapeutically (analgesically) effective dose of intravenous opioid analgesic to the patient if the patient requests analgesia before the second dose of tramadol, to provide effective analgesia to the patient(s).

In preferred embodiments where the tramadol is administered for the treatment of post-operative pain, the treatment of pain in the patient is opioid-sparing over the first 48 hours post-surgery.

In other preferred embodiments, the human patient(s) suffering from pain is unable to ingest an oral dosage form (e.g., of tramadol or another opioid analgesic and/or an NSAID) because the patient is suffering from cancer pain.

In accordance with the above, the final drug product (containing the intravenous dose of tramadol) may be presented as, e.g., as unit-dose ampoules, unit-dose vials, multi-dose ampoules, multi-dose vials, and drug in pre-mixed bags.

In certain preferred embodiments, the M1 metabolite of tramadol (0-desmethyltramadol) contributes to analgesic effect provided by the present invention (dosing regimen), without being toxic (e.g., without significant side effects) to humans at the administered dose of intravenous tramadol.

In certain embodiments, the method may provide a faster onset of pain relief than oral doses of 100 mg tramadol HCl given every 6 hours.

The invention is further directed in part to the above methods, wherein the safety and tolerability of tramadol for treating pain in human patients is improved.

In certain preferred embodiments, the pharmacokinetic profile (e.g., Cmax) achieved by this 45-80 mg, preferably about 60 mg IV tramadol dosing regimen at a time where the patient might be switched to oral meds (e.g., after the 44-48 hour dosing interval) is similar to the pharmacokinetic profile (e.g., Cmax) provided at steady-state by a dosing regimen of 100 mg tramadol HCl administered orally every 6 hours. This allows the patient to be stepped down from the intravenous tramadol dosing regimen to an oral dosing regimen. In turn, this allows the patient to be discharged from hospital care with less concern about deleterious effects which might occur from a switch from intravenous to oral analgesic medicine (e.g., the switch to an oral version of the drug providing a much different Cmax).

The term “about 60 mg” should be construed with the goal of the present invention in mind—the dose of the dose (“about”) may be adjusted to a limited degree, e.g., as long as the goal of a mean Cmax which is similar to the mean steady-state Cmax that is obtained via the administration of an oral dosing regimen of 100 mg tramadol administered to human patients every 6 hours (if the dosing regimen is continued for 48 hours). Generally speaking, it should be recognized that the a dose(s) of the drug may be modified (e.g., intravenous tramadol may be modified, e.g., to a dose from about 45 mg to about 80 mg and intravenous acetaminophen may be modified to a dose from about 500 mg to about 1000 mg, or from about 650 mg to about 750 mg) and a dosing interval for the second dose and onward of intravenous tramadol/acetaminophen may be modified, e.g., as long as the goal of a mean Cmax of tramadol is obtained which is similar to the mean steady-state Cmax is obtained via the administration of an oral dosing regimen of 100 mg tramadol administered to human patients every 6 hours (if the dosing regimen is continued for 48 hours) in order to provide treatment of pain (e.g., acute pain) in the human patient(s).

In additional embodiments, the invention is directed to a method of reducing surgical pain in human patients, comprising administering the intravenous dosing regimen of tramadol and acetaminophen as described herein, such that the patient experiences relief from pain associated with the surgery. In preferred embodiments, the method further comprises intravenously co-administering a 60 mg dose of intravenous tramadol and about a 650 to about 750 mg dose of acetaminophen about every six hours post-operatively to the patient. Preferably, the intravenous tramadol/acetaminophen therapy is continued until the patient no longer is suffering from post-operative pain.

Additional embodiments of the present invention are directed to a kit, comprising a vial containing an intravenous dose of tramadol or a pharmaceutically acceptable salt thereof in an amount from about 45 mg to about 80 mg (based on the hydrochloride salt); and a vial containing an intravenous dose of acetaminophen in an amount from about 500 mg to about 1,000 mg. In certain embodiments, the kit contains additional doses of tramadol and acetaminophen. In certain preferred embodiments, the kit contains sufficient doses of tramadol and acetaminophen to be administered about every 5 to about every 7 hours (e.g., about every 6 hours) until the patient no longer requires treatment with intravenous tramadol, e.g., up to about 48 hours after initiation of dosing (e.g., about 8 doses of each drug). In certain embodiments, the doses of tramadol HCl and acetaminophen are contained within the same vial, and the kit contains separate vials for each dosing interval, e.g., until the patient no longer requires treatment with intravenous tramadol, e.g., up to about 48 hours after initiation of dosing (e.g., about 8 doses). In other embodiments, the doses of tramadol HCl and acetaminophen are contained within separate vials, and the kit contains vials for each dosing interval, e.g., until the patient no longer requires treatment with intravenous tramadol, e.g., up to about 48 hours after initiation of dosing (e.g., about 8 doses). The intravenous dosing regimen contained in the kit preferably provides a Cmax of tramadol which is similar to the Cmax of an oral dose of 100 mg tramadol HCl given every 6 hours at steady-state. In certain preferred embodiments, each dose of tramadol is about 60 mg. In certain preferred embodiments, each dose of acetaminophen is from about 650 mg to about 750 mg.

The methods of the present invention are described in further detail in the following sections. However, it should be understood that for purposes of the present invention, the following terms have the following meanings:

The term “acute pain” as used herein means pain that has a sudden onset and commonly declines over a short time (days, hours, minutes) and follows injury to the body and which generally disappears when the bodily injury heals.

The term “effective analgesia” is defined for purposes of the present invention as a satisfactory reduction in or elimination of pain, along with the process of a tolerable level of side effects, as determined by the human patient.

The term “effective pain management” means for purposes of the present invention as the objective evaluation of a human patient's response (pain expressed versus side effects) to analgesic treatment by a physician as well as subjective evaluation of therapeutic treatment by the patient undergoing such treatment. The skilled artisan will understand that effective analgesia will vary according to many factors, including individual patient variations.

The term “breakthrough pain” means pain which the patient experiences despite the fact that the patient is being administered generally effective amounts of, e.g., an opioid analgesic such as buprenorphine.

The term “rescue” refers to a dose of an analgesic which is administered to a patient experiencing breakthrough pain.

An “effective amount” is an amount sufficient to effect beneficial or desired clinical results including alleviation or reduction in pain. In some embodiments, the “effective amount” may reduce the pain of ongoing pain and/or breakthrough pain (including ambulatory pain and touch-evoked pain).

The term “parenterally” as used herein includes subcutaneous injections, intravenous, intramuscular, intrasternal injection or infusion techniques.

The term “patient” as used herein refers to a warm blooded animal such as a mammal which is the subject of trauma, e.g., surgical trauma. It is understood that at least humans, dogs, cats, and mice are within the scope of the meaning of the term.

As used herein, the term “treat” or “treatment”, or a derivative thereof, contemplates partial or complete inhibition of acute pain, when a composition of the present invention is administered following the onset of acute pain.

All numbers expressing quantities of ingredients, reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should be construed in light of the number of significant digits and ordinary rounding approaches.

As used herein a “dosage regimen” refers to the protocol used to administer an intravenous pharmaceutical formulation comprising ibuprofen to a patient. In some embodiments the dosage regimen comprises a dose amount and dosing interval.

DETAILED DESCRIPTION

The chemical name for tramadol is (±)cis-2-[(dimethylamino)methyl]-1-(3-methoxyphenyl) cyclohexanol hydrochloride [or (1R,2R)-rel-2-[(dimethyl-amino)methyl]-1-(3-methoxyphenyl) cyclohexanol hydrochloride, (1RS, 2RS)-2-[(dimethylamino)methyl]-1-(3-methoxyphenyl) cyclohexanol hydrochloride, (±)-(RR, SS)-2-[(dimethylamino)methyl]-1-(3-methoxyphenyl) cyclohexanol hydrochloride]. Unless otherwise specified, the term tramadol refers to the racemic mixture of the (±)cis isomers.

Tramadol is a centrally-acting synthetic analgesic of the aminocyclohexanol group with opioid-like effects. Tramadol is extensively metabolized following administration resulting in a number of enantiomeric metabolites which display different opioid-receptor binding properties, and monoaminergic reuptake inhibition (Grond and Sablotzki, 2004). Both enantiomers of tramadol and (+)-M1 are responsible for the analgesic effect. The primary metabolite [(+)-M1 or (+)-O-desmethyltramadol] of tramadol confers significant μ-opioid activity; (+)-tramadol confers weak μ-opioid activity and significant serotonin reuptake inhibition; and (−)-tramadol is responsible for the inhibition of noradrenaline re-uptake (Gillen et al., 2000; Raffa, 2008). Nonclinical studies have shown that antinociception induced by tramadol is only partially antagonized by the opiate antagonist, naloxone, indicating that non-opioid mechanisms are also involved in its pharmacodynamic action (Collart et al., 1992).

Tramadol has efficacy in management of acute postoperative pain equivalent to morphine and other opioids administered intravenously, although the onset of action for tramadol is slower. The parenteral route has the advantage of immediate bioavailability and faster onset of action than oral, and is available to postoperative patients who cannot take oral medications. Current standard-of-care injectable analgesics (opioids and NSAIDs) have significant adverse effects, including opiate-induced respiratory depression, excessive sedation, hypotension, dependency, increased bleeding risk, renal toxicity and gastrointestinal irritation, which can potentially slow the postoperative rehabilitation process and compound the risk inherent in any surgical procedure.

Tramadol is currently commercially available in various countries/territories in the following forms: 50 mg/ml or 100 mg/2 ml, solution for injection; 50 mg, capsules, hard; 50 mg, prolonged-release tablets; 100 mg, prolonged-release tablets; 150 mg, prolonged-release tablets; 200 mg, prolonged-release tablets; 50 mg, tablets; 100 mg/ml, oral drops, solution; and 100 mg, suppositories. In the U.S., tramadol is approved by the Food and Drug Administration (FDA) and marketed as an oral capsule/tablet for moderate to moderately severe pain in adults, e.g., under the tradename Ultram® (tramadol hydrochloride tablets).

Parenteral tramadol has been used extensively in Europe and other areas of the world for the amelioration of postoperative pain in both adults and children. The efficacy of tramadol has been thoroughly reviewed (Lee C R, McTavish D, Sorkin E M. Tramadol. A preliminary review of its pharmacodynamic and pharmacokinetic properties, and therapeutic potential in acute and chronic pain states. Drugs. 1993; 46:313-340; Scott J L, Perry C M. Tramadol. A review of its use in perioperative pain. Drugs. 2000; 60:139-176; Grond S and Slabotzi A. Clinical pharmacology of tramadol. Clin Pharmacokinet. 2004; 43:879-923). Parenteral tramadol in such territories consists of tramadol 50 mg or 100 mg administered as a slow bolus injection (over 2-3 minutes) every 4-6 hours.

Acetaminophen is a non-salicylate antipyretic and non-opioid analgesic agent. Its chemical name is N-acetyl-p-aminophenol. Acetaminophen injection is indicated for the management of mild to moderate pain; the management of moderate to severe pain with adjunctive opioid analgesics; and the reduction of fever. Acetaminophen injection is available in the U.S. under the tradename Ofirmev™ from Cadence Pharmaceuticals, Inc. It is supplied in a 100 mL glass vial containing 1000 mg acetaminophen (10 mg/mL) and the vials are approved for single use only. Acetaminophen injection can be administered, e.g., as a 15 minute infusion or as a 30 minute infusion, and may be administered every 4 to 6 hours. The maximum recommended dose of acetaminophen on a daily basis to adults is 4000 mg. Ofirmev injection is a sterile, clear, colorless, non-pyrogenic, isotonic formulation of acetaminophen for intravenous infusion. It is a pH of about 5.5 and an osmolality of about 290 mOsm/kg. Each 100 mL contains 1000 mg acetaminophen, USP, 3840 mg mannitol, USP, 25 mg cysteine hydrochloride, monohydrate, USP, 10.4 mg dibasic sodium phosphate, anhydrous, USP. The pH is adjusted with hydrochloric acid and/or sodium chloride. The dosage of Ofirmev for adults and adolescents weighing 50 kg and over is 1000 mg every 6 hours or 650 mg every 4 hours, with a maximum single dose of Ofirmev of 1000 mg and a minimum dosing interval of 4 hours and a maximum daily dose of acetaminophen of 4000 mg per day. For adults, adolescents weighing under 50 kg, and children from 2 to 12 years of age, the recommended dosage of Ofirmev is 15 mg/kg every 6 hours or 12.5 mg/kg every 4 hours, with a maximum single dose of Ofirmev of 15 mg/kg, and a maximum daily dose of acetaminophen of 75 mg/kg per day.

In certain preferred embodiments, the intravenous tramadol and acetaminophen doses are administered intravenously at the same time post-surgery, at dosing intervals of every 4 to about every 6 hours. In certain preferred embodiments, the tramadol and acetaminophen doses are contained within a single unit dose, e.g., inside a vial.

The invention is further directed to a method of treating at post-surgical patient in need of pain relief comprising administering to the patient an intravenous pharmaceutical composition comprising intravenous tramadol together with intravenous acetaminophen. In certain preferred embodiments of this method, the dose of acetaminophen produces a decreased need for tramadol and/or a additional opioid analgesic, decreased side effects from use of a narcotic analgesic and/or decreased perception of pain.

The co-administration of intravenous tramadol and acetaminophen used in accordance with the invention provides a treatment for pain and/or fever using the intravenous route of administration, and is useful, e.g., for the treatment of mild to severe pain (and particularly acute pain) in adults and children over 12 years of age. Co-administration of intravenous tramadol and acetaminophen used in accordance with the methods of the invention provides pain control, e.g., for abdominal and orthopedic surgical procedures; may be opioid sparing when used for post-operative pain; may provide a reduction in opioid side effects; provides a reduction in adverse events, may provide a reduction in the need for anti-emetic medications, may allow patients to become ambulatory faster.

The co-administration of intravenous tramadol and acetaminophen in accordance with the present invention may provide the following benefits, for example: speeds relief of pain to expedite release from a hospital or hospital-like setting; speeds relief to expedite hospital release, as demonstrated by a fast reduction of mild to severe pain in adults and children over 12 years of age; a reduction in pain at rest and with movement as measured by visual analog scores (VAS) following abdominal and orthopedic surgeries; a reduction in opioid side effects (nausea, vomiting, constipation); preferably does not cause bleeding or renal concerns; and may provide an improvement in time to ambulation which may enable facilities to schedule additional procedures in the ambulatory setting.

Surgical procedures often result in some form of acute pain. Surgical pain may include nociceptive, neuropathic or psychological components. Nociceptive pain is a pain experienced as a result of nociception, which is detection of a stimulus by a pain receptor (nociceptor) and transmission of the information to the brain along nerves. Nociceptive pain is caused by tissue damage and inflammation in response to trauma. The resulting pain is usually not well localized and is opioid responsive.

Several options are available for postoperative pain management (Singelyn et al., 1998; Sinatra et al., 2002). Options include intermittent “on-demand” analgesia, continuous epidural analgesia with opioids and/or local anesthetics is effective, or to provide a combination of nerve blocks with long-acting local anesthetics and/or opioids initiated intra-operatively and continued into the immediate postoperative period. In the United States (US) and in India, this latter strategy is frequently employed, and most TKA and THA procedures are currently performed with regional (or neuraxial) or other nerve blocks and without general anesthesia. Each of these options for postoperative pain management can be used concomitantly with the intravenous tramadol treatments described herein as recue medicine to treat breakthrough pain.

The present invention is directed in part to tramadol and acetaminophen in a pharmaceutically acceptable sterile solution formulation(s) containing an effective dose of tramadol or a pharmaceutically acceptable salt thereof, either in combination with an effective dose of acetaminophen or in separate intravenous formulations and a method of administration of the same for the treatment of pain, e.g., postoperatively. Tramadol injection and acetaminophen injection in accordance with the present invention will fulfill an important need by providing a safe and effective alternative injectable analgesic for use in the acute postoperative setting.

Preferably, the dose of tramadol administered in accordance with the present invention is, e.g., from about 45 mg to about 80 mg, and in certain preferred embodiments from about 45 to about 55 mg, or from about 70 to about 80 mg, or from about 55 to about 65 mg. In certain preferred embodiments, each tramadol dose administered is in the amount of, e.g., 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79 or 80 mg, e.g., provided as tramadol hydrochloride. The tramadol may be provided, e.g., as 60 mg tramadol hydrochloride/1 ml. The injectable tramadol dose is generally intended for in-hospital use, although it can be used in other settings. In certain preferred embodiments, the tramadol is administered intravenously over a time period from about 10 minutes to about 3 hours. In certain preferred embodiments, the therapeutically effective dose of tramadol intravenously over a time period from about 10 minutes to about 20 minutes, and most preferably in certain embodiments about 15 (±2) minutes. Thus, in preferred embodiments, the therapeutically effective dose of tramadol intravenously over a time period from about 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 minutes.

The dose of acetaminophen is preferably administered intravenously simultaneously with the dose of tramadol. The dose of acetaminophen may be from about 500 to about 1000 mg, preferably from about 650 g to about 750 mg. In certain preferred embodiments, the dose of acetaminophen is 650, 655, 660, 665, 670, 675, 680, 685, 690, 695, 700, 705, 710, 715, 720, 725, 730, 735, 740, 745, or 750 mg, i.e., any integer from about 650 mg to about 750 mg.

Further aspects of the invention are directed to diluting the dose of tramadol and acetaminophen in from about 50 ml to about 100 ml of a pharmaceutically acceptable fluid for injection (such as normal saline), and standardizing the administration of the injection of the dose of tramadol via the use of a pump. In preferred embodiments, the pump is an infusion pump that is commercially available, such as pumps available from Braun and Hospira.

As previously mentioned, the dose of tramadol administered in accordance with the present invention may be diluted in a suitable pharmaceutically acceptable carrier for injection. Examples of such include sterile water for injection, normal saline, etc. Intravenous fluids are well known to those of ordinary skill in the art, and may include other ingredients beyond the dose of tramadol and the carrier/solvent for the tramadol, e.g., sterile solutions of simple chemicals such as sugars, amino acids or electrolytes, which can be easily carried by the circulatory system and assimilated. Such fluids are typically prepared with water for injection USP. Fluids used commonly for intravenous (IV) use are disclosed in Remington, The Science and Practice of Pharmacy [full citation previously provided], and include: alcohol, e.g., 5% alcohol (e.g., in dextrose and water (“D/W”) or D/W in normal saline solution (“NSS”), including in 5% dextrose and water (“D5/W”), or D5/W in NSS); synthetic amino acid such as Aminosyn, FreAmine, Travasol, e.g., 3.5 or 7; 8.5; 3.5, 5.5 or 8.5% respectively; ammonium chloride e.g., 2.14%; dextran 40, in NSS e.g., 10% or in D5/W e.g., 10%; dextran 70, in NSS e.g., 6% or in D5/W e.g., 6%; dextrose (glucose, D5/W) e.g., 2.5-50%; dextrose and sodium chloride e.g., 5-20% dextrose and 0.22-0.9% NaCl; lactated Ringer's (Hartmann's) e.g., NaCl 0.6%, KCl 0.03%, CaCl₂) 0.02%; lactate 0.3%; mannitol e.g., 5%, optionally in combination with dextrose e.g., 10% or NaCl e.g., 15 or 20%; multiple electrolyte solutions with varying combinations of electrolytes, dextrose, fructose, invert sugar Ringer's e.g., NaCl 0.86%, KCl 0.03%, CaCl₂) 0.033%; sodium bicarbonate e.g., 5%; sodium chloride e.g., 0.45, 0.9, 3, or 5%; sodium lactate e.g., ⅙ M; and sterile water for injection The pH of such IV fluids may vary, and will typically be from about 3.5 to about 8 as known in the art.

The dose of tramadol or pharmaceutically acceptable salts thereof and acetaminophen can be administered alone or in combination with other medical treatments, or other therapeutic agents, such as NSAIDs. When so-used, other therapeutic agents can be administered before, concurrently (whether in separate dosage forms or in a combined dosage form), or after administration of an active agent of the present invention.

Consistent with the known clinical effects of opioids, nonclinical safety pharmacology studies have shown that tramadol at high doses affects the central nervous system (CNS), producing sedation, impaired mobility, vomiting (dogs), decreased activity, and convulsions (Matthiesen et al., 1998). Also consistent with clinical effects, changes in blood pressure have been observed in cardiovascular studies in rats at high doses (Raimundo et al., 2006). Tramadol use, particularly with high doses, has been associated with seizures, and the risk of seizures is increased in the presence of drugs that reduce seizure threshold, head trauma or prior history of seizures.

The toxicity of tramadol has been summarized by Matthiesen, et al. (1998). The single-dose toxicity of tramadol was similar in all species tested, independent of the route of administration. Notable acute findings included restlessness, unsteady gait, reduced spontaneous activity, exophthalmus, mydriasis, salivation, vomiting (dog), tremor, convulsions, slight cyanosis and dyspnea. The principle findings in repeat-dose toxicity studies in rats and dogs were behavioral/clinical signs and convulsions at doses of ≥25 mg/kg/day. The kidney and liver were identified as potential target organs in rats, with mild effects (minimal tubular vacuolization and perivenular hydropic degeneration, respectively) following repeat intraperitoneal dosing at high doses of tramadol.

There was no evidence of genotoxic potential for tramadol in standard in vitro and in vivo studies (Matthiesen et al., 1998). Carcinogenicity bioassays in mice and rats showed no evidence of carcinogenic potential. An extensive reproductive and teratology program revealed no safety concerns with respect to fertility or teratogenic effects after oral administration (Matthiesen et al., 1998; Yamamoto et al., 1972). Toxicity to offspring only occurred at doses associated with maternal toxicity.

Following oral administration, tramadol is rapidly and almost completely absorbed. The pharmacokinetics of tramadol were evaluated in healthy male volunteers (n=10) in a crossover design using 100 mg PO or IV doses (Lintz et al., 1986). Peak serum concentrations (tmax) were reached approximately 2 hours after oral dosing and the peak serum concentration (Cmax) for PO tramadol was 280±49 ng/mL. The terminal half-life was 5.1 hours for PO and 5.2 hours for IV administration. The area under the serum tramadol concentration-time curve (AUC) was 2488±774 ng·h/mL for PO and 3709±977 ng·h/mL for IV administration. Total clearance was 467±124 mL/min for PO and 710±174 mL/min for IV administration. The absolute bioavailability of the oral dose was 68±13%, based on comparison of the AUC values, while the estimated absorption of the oral dose was 86-88%. The difference between absorption and bioavailability was attributed to first pass metabolism, which was estimated to be ˜20%. However, the absolute bioavailability approaches 90-100% with continuous dosing, probably due to saturation of first pass metabolism (Liao et al., 1992). Other studies have corroborated these findings (Grond and Sablotzki, 2004).

The pharmacokinetic profile of tramadol following i.v. and p.o. administration in humans (n=10, male) is summarized in Table A below (Lintz W, Barth H, Osterloh O, Schmidt-Bothelt E. Bioavailability of enteral tramadol formulations. 1st communication: capsules. Arzneim Forsch Drug Res. 1986; 36:1278-1283). The absolute oral bioavailability of tramadol was 68% (±13) in humans.

TABLE A Pharmacokinetics of Tramadol (100 mg) Following Intravenous and Oral Administration to Humans Tramadol C_(max) AUC_(0-24 h) CL/F (100 mg) (ng/mL) t₁/₂ (h) (ng · h/mL) V_(d) (L) (mL/min) i.v. — 5.2 ± 0.8 3709 ± 977 203 ± 40 467 ± 124 p.o 280 ± 49 5.1 ± 0.8 2488 ± 774 306 ± 52 710 ± 174 Abbreviations: C_(max), maximal concentration; t₁/₂, half-life; AUC, area under the plasma concentration-time curve; CL, clearance; F, bioavailability; V_(d;) volume of distribution

The pharmacokinetic profile of tramadol and the (+)-M1 and (−)-M1 metabolites was also evaluated in humans (N=12, male) following p.o. administration of a single 1.5 mg/kg dose of tramadol (Matthiesen, et al., 1993). The data are summarized in Table B below:

TABLE B Pharmacokinetics of Tramadol and the (+) and (−) Enantiomers of the M1 Metabolite Tramadol (1.5 CL/F mg/kg, C_(max) T_(max) AUC (mL/min/ [100 mg]) (ng/mL) (h) t₁/₂ (h) (ng · h/mL) kg) Tramadol 274 ± 75 1.6 ± 0.5 5.9 ± 0.7 2177 ± 722 742 ± 234 (+)-M1 147 ± 39 1.6 ± 0.5 6.0 ± 1.0 1258 ± 410 642 ± 204 (−)-M1 125 ± 32 1.5 ± 0.5 5.2 ± 0.8  908 ± 298 883 ± 264 Abbreviations: C_(max), maximal concentration; T_(max), time to maximal concentration; AUC, area under the plasma concentration-time curve; CL, clearance; F, bioavailability; t₁/₂, half-life; V_(d); volume of distribution

Tramadol undergoes hepatic metabolism and both the parent drug and the active metabolite are excreted by the kidneys. The active metabolite, M1 (O desmethyltramadol), is produced by the action of CYP2D6 isozyme of the cytochrome P450 enzyme system. It has a half-life of approximately 6.7 hours after oral administration (single dose of 100 mg), compared to a half-life of 5.6 hours for tramadol administered intravenously. Hepatic impairment results in decreased metabolism of both the parent compound and the active metabolite. Tramadol is rapidly distributed after IV administration with a distribution half-life in the initial phase of 0.31±0.17 hours, followed by a slower distribution phase with a half-life of 1.7±0.4 hours (Lintz et al., 1986). The volumes of distribution following PO and IV administration were 306 L and 203 L, respectively, indicating that tramadol has a high tissue affinity. The protein binding of tramadol is approximately 20%; however, saturation of binding sites does not occur in the therapeutic dose range (Ultram® Prescribing Information, 2009).

Elimination half-life increases approximately 2-fold in subjects with renal or hepatic impairment. Patients who metabolize drugs poorly via CYP2D6 (Caucasian population prevalence ˜8%) may obtain reduced benefit from tramadol due to reduced formation of M1 (Ultram® Prescribing Information, Ortho-McNeil-Janssen Pharmaceuticals, Inc, 2009).

Studies of IV tramadol in the postoperative setting have shown an acceptable safety profile. Loading doses up to 150 mg IV were not associated with any serious adverse effects (Silvasti et al., 2000). Also, no serious adverse effects were observed in clinical trials of tramadol with mean (±SD) cumulative doses of 449±66 mg (Rud et al., 1994), 677±473 mg (range 128-1750 mg) (Silvasti et al., 2000), and 868.3±412.2 mg (Pang et al., 1999) over 24, 36 and 48 h respectively.

The most common adverse events, nausea, dizziness, headache, somnolence, sweating, fatigue, constipation, dry mouth and vomiting, which are usually mild to moderate in severity and only occasionally lead to premature discontinuation of tramadol.

The Ultram® and Tramal® labels contain several warnings and precautions regarding use of tramadol. The risk of most of these potential adverse events can be minimized by decreasing the dose or excluding use of tramadol in subjects with risk factors associated with these known, rare adverse events. Tramadol metabolism is reduced in the setting of advanced cirrhosis and renal clearance of both tramadol and its metabolites is reduced in individuals with creatinine <30 mL/min. Thus, the dose of tramadol should be reduced by half or the interval doubled in these populations. Dosage adjustment is also recommended in individuals >75 years of age as they have reduced drug clearance. Tramadol is metabolized by CYP2D6 and CYP3A4; thus, drugs that are inhibitors or inducers of these enzymes can alter tramadol metabolism, resulting in decreased efficacy and/or increased risk of seizures or other adverse effects. Tramadol is associated with a low risk for respiratory depression, which is increased in the presence of other opioids, anesthetic agents and other CNS depressants, including alcohol. Respiratory depression due to the opioid activity of tramadol can be reversed with naloxone. Naloxone should be used cautiously as it can potentiate seizures when administered with tramadol. The full range of allergic/hypersensitivity reactions have been reported in association with tramadol administration, including serious and rarely fatal anaphylactoid reactions.

Potentially life-threatening serotonin syndrome may occur with tramadol products with concomitant use of serotonergic drugs such as SSRIs, tricyclic antidepressants, monoamine oxidase inhibitors and triptans.

Tramadol use, particularly with high doses, has been associated with seizures, and the risk of seizures is increased in the presence of drugs that reduce seizure threshold, head trauma or prior history of seizures.

Human studies evaluating the abuse potential of tramadol, administered via IV or PO routes, have also been conducted (Epstein et al., 2006). During the initial dose-ranging studies, seizure was observed following a tramadol dose of 700 mg IV administered over 1 minute and 300 mg IV delivered over 2.5 minutes. No seizures were observed with a tramadol dose of 200 mg IV administered over 5 minutes. The authors hypothesized that toxicity is likely to limit abuse of high doses of IV tramadol. In a subsequent study involving 10 experienced opioid abusers, tramadol (100 and 200 mg IV), morphine (10 and 20 mg IV) and placebo were administered over 5 minutes. The endpoints in the study were subjective; the extent to which subjects “liked” the effects of the drugs, as well as their ability to produce effects common to morphine and benzadrine (assessed by the Addiction Research Center Inventory-Morphine Benzadrine Group [ARCI-MBG] scale). Tramadol and morphine significantly increased ratings of “feel drug effect” compared to placebo. However, neither dose of tramadol increased ratings on the “liking” or ARCI-MBG scale or on any other subjective measure of opiate-like effects. In contrast, morphine 10 and 20 mg doses significantly increased ratings of “liking” and the morphine 20 mg dose increased ratings on the ARCI-MBG scale. Thus, tramadol administered via the parenteral route (IV or IM) is unlikely to be associated with the subjective morphine-like and positive mood effects typical of abuse and addiction.

In accordance with the present invention, it is desirable to provide an intravenous dosing regimen of tramadol which at steady-state provides a plasma concentration with respect to Cmax that is similar or equivalent to the steady-state Cmax provided by a 100 mg oral tramadol dose given every 6 hours would be desirable and would be safer and have less likelihood of significant side effects than, e.g., the administration of 100 mg of tramadol intravenously administered every 6 hours (i.e., same dose and dosing interval as the oral reference standard, Ultram®. It is further believed that it would desirable for such an intravenous dosing regimen(s) to provide a steady-state trough plasma level of tramadol (e.g., Cmin) which is at least as high as the steady-state trough level provided by a 100 mg oral tramadol dose given every 6 hours. The steady-state Cmax of the 100 mg oral dose of tramadol administered every 6 hours is about 736 ng/mL. For purposes of the present invention, a similar or equivalent Cmax provided by an intravenous tramadol dosing regimen would provide a Cmax within the range from about 80% to about 125% of the steady-state Cmax of the 100 mg oral tramadol administered every 6 hours (e.g., 736 ng/mL; or e.g., from about 588.8 ng/mL to about 920 ng/mL). It is especially preferred that the steady-state Cmax of the dosing regimen(s) of the present invention do not exceed the concentration provided by 100 mg oral tramadol administered every 6 hours, at steady-state (e.g., about 701 ng/mL) by more than 15% or more than about 10%. The co-administration of the acetaminophen in effective amounts, e.g, as described herein, is believed to further provide a synergistically improved analgesia than the dose of tramadol alone, and allows for less tramadol to be administered than would otherwise be required to treat pain in the human patient.

U.S. Pat. No. 9,693,949 (hereby incorporated by reference in its entirety) describes a method of administering tramadol for treating pain in a human patient(s) via an intravenous dosing regimen comprising intravenously administering a first dose of tramadol to a human patient(s) in an amount of about 50 mg; intravenously administering a second dose of tramadol to the human patient(s) in an amount of about 50 mg at about 2 hours after the first dose; intravenously administering a third dose of tramadol to the human patient(s) in an amount of about 50 mg at about 2 hours after the second dose; and thereafter intravenously administering additional doses of tramadol to the human patient(s) in an amount of about 50 mg tramadol at dosage intervals of about 4 hours, until the patient no longer requires treatment with tramadol, wherein the tramadol is tramadol base or a pharmaceutically acceptable salt of tramadol. By virtue of this state-of-the-art dosing regimen, tramadol is intravenously administered seven times on day one of therapy and six times a day thereafter. Thus, as per the above, the '949 patent teaches the intravenous administration of about 350 mg tramadol on day 1 and 300 mg tramadol on day 2 and onward. This is in comparison to the dosing regimen of the present invention, wherein the amount of intravenous tramadol given on a daily basis is about 240 mg. Likewise, with respect to acetaminophen, the dose administered via the present invention on a daily basis will be from about 2600 mg to about 3000 mg versus about 4000 mg per day, as currently approved for administration in the U.S. It is believed that three is no IV tramadol dosage regimen of 60 mg tramadol administered every 6 hours approved or use anywhere in the world.

In the present invention, the co-administration of acetaminophen at the same dosage interval as the tramadol (e.g., about every 6 hours), allows for the administration of less tramadol while preferably achieving the same or even better efficacy because of synergistic and non-overlapping mechanisms, despite the reduction in doses of each drug.

A further benefit of the present invention is that the dosing of tramadol and acetaminophen may be simultaneous. If a healthcare provider desired to administer, e.g., seven doses of tramadol on the first day of treatment (in accordance with the '949 patent) and four doses of acetaminophen (e.g., as per the package insert/administration directions for Ofirmev, 1000 mg every 6 hours), the healthcare provider would be administering 11 infusions (each about 15 minutes long) on day one and 10 infusions (each about 15 minutes long) on day 2. Instead, as per the present invention, the healthcare provider may administer both drugs only four times a day (about every 6 hours; about 15 minute infusions).

By virtue of the present dosing regimen comprising 60 mg IV tramadol every 6 hours, the maximum plasma concentration (Cmax) of the tramadol rapidly approaches the maximum concentration found at steady-state with respect to a dosing regimen of 100 mg tramadol HCl administered orally every 6 hours. The Cmax obtained after a number of doses of 60 mg IV tramadol (e.g., after the fourth, fifth, sixth or seventh dose) is approximately the same as the Cmax at steady-state for a dosing regimen of 100 mg tramadol HCl administered orally every 6 hours. However, in contrast, the oral tramadol dosing regimen takes considerably longer (Cmax₄₄₋₄₈) to reach that maximum tramadol plasma concentration. As discussed in Example 5 of the '949 patent, the Cmax of the 50 mg IV tramadol dosing regimen is about 736 ng/mL±152 and is approached during the third dose (see, e.g., Example 5, Table 11 and FIGS. 11-12), whereas the Cmax of tramadol for the oral 100 mg dosing regimen is about 701 ng/ml±178 and occurs at 42-48 hours after the first oral dose is administered (see, e.g., Example 5, Table 11 and FIGS. 9 and 12). Moreover, in this embodiment the trough levels (plasma concentrations of tramadol) also much more rapidly reach a level similar to the trough levels at steady-state for the oral 100 mg every 6 hours dosing regimen. It is believed that the fact that (for the 60 mg IV dosing regimen) peak and trough plasma levels similar to steady-state levels found for the oral 100 mg q6h dosing regimen are reached at a such an earlier time may translate into improved efficacy (pain relief) for the patients.

It is further believed that the intravenous dosing regimen of the invention, e.g., as a slow push of a therapeutically effective dose of tramadol contained in a bag over a time period from about 10 to about 20 minutes, preferably about 15 minutes, will provide added safety with respect to the above-mentioned potential adverse events and others, and will provide lower incidence of side effects associated with tramadol administration. It is further believed that the intravenous dosing regimen of the invention where a therapeutically effective dose of tramadol is administered to a human patient(s) over a time period from about 24 hours to 48 hours in much slower infusion will also provide these benefits.

The intravenous tramadol formulation in accordance with the invention typically includes tramadol in the form of its hydrochloride salt. However, one of ordinary skill in the art will appreciate that other forms of tramadol may be used, including but not limited to all pharmaceutically acceptable salts of tramadol. Such pharmaceutically acceptable salts may include, but are not limited to, metal salts such as sodium salt, potassium salt, secium salt and the like; alkaline earth metals such as calcium salt, magnesium salt and the like; organic amine salts such as triethylamine salt, pyridine salt, picoline salt, ethanolamine salt, triethanolamine salt, dicyclohexylamine salt, N,N′-dibenzylethylenediamine salt and the like; inorganic acid salts such as hydrochloride, hydrobromide, sulfate, phosphate and the like; organic acid salts such as formate, acetate, trifluoroacetate, maleate, tartrate and the like; sulfonates such as methanesulfonate, benzenesulfonate, p-toluenesulfonate, and the like; amino acid salts such as arginate, asparginate, glutamate and the like.

It is contemplated that with respect to the inventive methods for the intravenous administration of tramadol as described herein, other analgesics, preferably opioid analgesics, may be used to treat postoperative pain in the patient(s), as well. It is particularly contemplated that one or more opioid analgesics will be administered post-surgically to the patient as rescue medicine in order to treat breakthrough pain that the patient may experience.

The term “opioid analgesic” refers to all drugs, natural or synthetic, with morphine-like actions. The synthetic and semi-synthetic opioid analgesics are derivatives of five chemical classes of compound: phenanthrenes; phenylheptylamines; phenylpiperidines; morphinans; and benzomorphans, all of which are within the scope of the term. Opioid analgesics which are useful in the present invention include all opioid agonists or mixed agonist-antagonists, partial agonists, including but not limited to alfentanil, allylprodine, alphaprodine, anileridine, benzylmorphine, bezitramide, buprenorphine, butorphanol, clonitazene, codeine, desomorphine, dextromoramide, dezocine, diampromide, diamorphone, dihydrocodeine, dihydromorphine, dimenoxadol, dimepheptanol, dimethylthiambutene, dioxaphetyl butyrate, dipipanone, eptazocine, ethoheptazine, ethylmethylthiambutene, ethylmorphine, etonitazene, fentanyl, heroin, hydrocodone, hydromorphone, hydroxypethidine, isomethadone, ketobemidone, levorphanol, levophenacylmorphan, lofentanil, meperidine, meptazinol, metazocine, methadone, metopon, morphine, myrophine, narceine, nicomorphine, norlevorphanol, normethadone, nalorphine, nalbuphene, normorphine, norpipanone, opium, oxycodone, oxymorphone, papaveretum, pentazocine, phenadoxone, phenomorphan, phenazocine, phenoperidine, piminodine, piritramide, propheptazine, promedol, properidine, propoxyphene, sufentanil, tilidine, mixtures of any of the foregoing, salts of any of the foregoing, and the like.

In certain preferred embodiments, opioid analgesics include morphine, oxycodone, codeine, dihydrocodeine, diacetylmorphine, hydrocodone, hydromorphone, levorphanol, oxymorphone, alfentanil, buprenorphine, butorphanol, fentanyl, sufentanyl, meperidine, methadone, nalbuphine, propoxyphene and pentazocine or pharmaceutically acceptable salts thereof. In certain preferred embodiments, the opioid agonist is morphine. Equianalgesic doses of these opioids are generally known to those persons having ordinary skill in the art.

In certain embodiments, the patient's need for additional analgesic treatment beyond the intravenous tramadol may be ascertained via the use of a surrogate measure of pain. Pain rating scales are used in daily clinical practice to measure pain intensity. The commonly used measurement scales include the Visual Analog Scale (VAS), the Graphic Rating Scale (GRS), the Simple Descriptor Scale (SDS), the Numerical Rating Scale (NRS), and the Faces Rating Scale (FRS). All of these scales have been documented as being valid measures of pain intensity. The three scales most commonly used in the U.S. are the numerical, word and faces scales. One preferred pain rating scale is the visual analog scale (VAS), a 10 cm. vertical or horizontal line with word anchors at the extremes, such as “no pain” on one end and “pain as bad as it could be” at the other. The patient is asked to make a mark along the line to represent pain intensity.

Alternatively, the graphic rating scale (GRS) is a variation of the visual scale which adds words or numbers between the extremes. Wording added might include “no pain”, “mild”, “severe”. The descriptor scale (SDS) is a list of adjectives describing different levels of pain intensity. For example pain intensity may be described as “no pain”, “mild”, “moderate” or “severe”. The numerical pain rating scale (NPRS) refers to a numerical rating of 0 to 10 or 0 to 5 or to a visual scale with both words and numbers. The patient is asked to rate the pain with 0 being no pain and 10 being the worst possible pain. The faces scale was developed for use with children. This scale exists in several variations but relies on a series of facial expressions to convey pain intensity. Grouping patients' rating of pain intensity as measured with a numerical scale ranging from 0 to 10 into categories of mild, moderate, and severe pain is useful for informing treatment decisions, and interpreting study outcomes. In 1995, Serlin and colleagues (Pain, 1995, 277-84) developed a technique to establish the cut points for mild, moderate, and severe pain by grading pain intensity and functional inference. Since then, a number of studies have been conducted to correlate the numerical scales, for example the NPRS, with cutpoints related to levels of pain intensity. Common severity cutpoints are (1 to 4) for mild pain, (5 to 6) for moderate pain, and (7 to 10) for severe pain.

Surrogate measures of opioid efficacy (analgesia) include sedation, respiratory rate and/or pupil size (via pupillometry), and visual analogue scale (“VAS”) for “drug effect”. The Sum of Pain Intensity Differences (SPID) through 48 hours post first dose (SPID48) at rest may be used as a primary measure of efficacy.

The intravenous tramadol/acetaminophen dosing regimens of the invention may be used in the in the hospital or day hospital setting and therefore administered by medical staff. The tramadol hydrochloride injection for intravenous use and its dosing regimen can fill an important need in addition to tramadol (e.g., ULTRAM®) tablets and tramadol (e.g., ULTRAM® ER) extended-release tablets by providing this safe and effective injectable analgesic with a novel mechanism of action (μ-opioid agonist and monoaminergic reuptake inhibition) for use in the acute post-operative setting. These dosing regimens may be used, e.g., for all types of surgery, including orthopedic surgery (e.g., total knee replacement, bunionectomy) or soft tissue surgery (e.g., elective abdominoplasty).

CONCLUSION

All patents and publications identified in the above paragraphs are hereby incorporated by reference in their entireties. It will be readily apparent to one of ordinary skill in the relevant arts that other suitable modifications and adaptations to the methods and applications described herein are suitable and may be made without departing from the scope of the invention or any embodiment thereof. While the invention has been described in connection with certain embodiments, it is not intended to limit the invention to the particular forms set forth, but on the contrary, it is intended to cover such alternatives, modifications and equivalents as may be included within the spirit and scope of the invention as defined by the following claims. All of the patents and publications cited herein are hereby incorporated by reference. 

What is claimed is:
 1. A method of administering tramadol for treating pain via an intravenous dosing regimen, comprising intravenously administering a first dose of tramadol to a human patient in an amount from about 45 mg to about 80 mg; and concurrently administering an intravenous dose of acetaminophen in an amount from about 500 mg to about 1000 mg; and thereafter intravenously administering the doses of tramadol and acetaminophen about every 6 hours until the patient no longer requires treatment with intravenous tramadol, wherein the tramadol is tramadol base or a pharmaceutically acceptable salt of tramadol.
 2. The method of claim 1, wherein the intravenous dosing regimen provides a Cmax of tramadol which is similar to the Cmax of an oral dose of 100 mg tramadol HCl given every 6 hours at steady-state.
 3. The method of claim 1, wherein each dose of tramadol is about 60 mg tramadol hydrochloride, and each dose of acetaminophen is from about 650 mg to about 750 mg.
 4. The method of claim 1, wherein each dose of tramadol is about 60 mg.
 5. The method of claim 4, the intravenous dosing regimen of the invention provide a Cmax of tramadol at steady-state that is from about 80% to about 125% of the Cmax provided at steady-state by a 100 mg oral dose of tramadol HCl given every 6 hours.
 6. The method of claim 4, wherein the intravenous dosing regimen provides a Cmax of tramadol at steady-state from about 80% to about 125% of about 736 ng/mL.
 7. The method of claim 1, further comprising continuing to administer additional doses of tramadol and acetaminophen to the human patient for at least about 42 hours after the first administered dose of tramadol.
 8. The method of claim 1, further comprising diluting the dose of tramadol and acetaminophen in from about 50 ml to about 500 ml of a pharmaceutically acceptable fluid for injection, and standardizing the administration of the injection of the dose of tramadol and acetaminophen via the use of a pump.
 9. The method of claim 8, wherein the dose is provided in the form of a sterile solution at a concentration of about 60 mg tramadol hydrochloride and from about 650 mg to about 750 acetaminophen contained in one or more ampoules.
 10. The method of claim 9, wherein the ampoules contain the dose of tramadol together acetaminophen with a buffering agent in water for injection.
 11. The method of claim 1, further comprising diluting the dose of tramadol and acetaminophen into an IV bag for administration to the human patient.
 12. The method of claim 1 wherein the patient is undergoing surgery, further comprising administering a first dose of tramadol/acetaminophen to the patient intra-operatively at wound closure, or from first demand of analgesia postoperatively, and administering further doses of intravenous tramadol/acetaminophen for at least two days post-surgery.
 13. The method of claim 1, wherein the human patient is suffering from acute post-operative pain.
 14. The method of claim 13, further comprising switching the human patient after at least three intravenous doses of tramadol/acetaminophen, to oral doses of the same amount of tramadol and acetaminophen previously administered intravenously, such that the Cmax of tramadol at the time the human patient is switched to oral doses is similar to the Cmax provided at steady-state by a dosing regimen of 100 mg tramadol HCl administered orally every 6 hours.
 15. The method of claim 1, further comprising administering an opioid analgesic which is not tramadol to the human patient to treat breakthrough pain.
 16. A method of administering tramadol for treating pain via an intravenous dosing regimen, comprising intravenously administering a first dose of tramadol to a human patient in an amount of about 60 mg; and concurrently administering an intravenous dose of acetaminophen in an amount of about 650 mg; and thereafter intravenously administering the doses of tramadol and acetaminophen about every 6 hours until the patient no longer requires treatment with intravenous tramadol, wherein the tramadol is tramadol base or a pharmaceutically acceptable salt of tramadol, such that the intravenous dosing regimen provides a Cmax of tramadol which is similar to the Cmax of an oral dose of 100 mg tramadol HCl given every 6 hours at steady-state.
 17. The method of claim 16, the intravenous dosing regimen of the invention provide a Cmax of tramadol at steady-state that is from about 80% to about 125% of the Cmax provided at steady-state by a 100 mg oral dose of tramadol HCl given every 6 hours.
 18. The method of claim 17, wherein the intravenous dosing regimen provides a Cmax of tramadol at steady-state from about 80% to about 125% of about 736 ng/mL.
 19. A kit, comprising a vial containing an intravenous dose of tramadol or a pharmaceutically acceptable salt thereof in an amount from about 45 mg to about 80 mg (based on the hydrochloride salt); and a vial containing an intravenous dose of acetaminophen in an amount from about 500 mg to about 1000 mg.
 20. The kit of claim 19, which contains additional doses of tramadol and acetaminophen. 